Hmm.. Does this page say your browser supports WebGL2? https://get.webgl.org/webgl2/
Also could you enter about:support in firefox location bar and find the value of WebGL 2 Driver Renderer?
What OS and Firefox version are you running?
Oh, hello fellow arch user :) I tried with the same firefox version, it works for me, so my best (and so far only) guess is something goes wrong with the graphics drivers somewhere.
I uploaded a linux build of the demo, does that work?
If you want to play in browser one more thing to try is disable hardware acceleration in firefox:
- Edit -> Settings
- use search box to find "use recommended performance settings"
- Uncheck, and then uncheck "Use hardware acceleration when available"
Restart firefox and try once more. You probably want to restore the setting after trying, though.